In the briny deep, far from shore, the vast darkness is home to tiny, glowing fish, massive jellies that may be the largest animals on the planet, and an untold number of other creatures.
What inhabits this realm of the ocean — from about 600 feet to about 3,000 feet — is so shrouded in mystery that scientists call it the “twilight zone.”

At the end of the week, a team of marine biologists, engineers, and other specialists from the Woods Hole Oceanographic Institution will embark on the first long-term study of this netherworld, a nearly lightless region believed to be teeming with life — perhaps more than the rest of the ocean combined.
“It’s the last frontier on Earth that’s truly not well understood,” said Andone Lavery, a senior scientist who will oversee the first expedition.
“We have many questions.”

Chief among them: What animals live there, and how many?
Do they play a role in helping regulate the planet’s climate, and if so, how?
Could these species provide a sustainable source of protein for the world’s growing population?
That last question may be the most controversial.

The scientists, who this year won a $35 million grant from a coalition of philanthropy groups called the Audacious Project, say they plan to spend the next six years mapping the biodiversity of the twilight zone before it’s exploited by the fishing industry.
But some environmental advocates have raised concerns about whether the research could have the opposite effect, opening something of a Pandora’s box by revealing to the industry what bounty lies below.
“There is a clear risk with shining a bright light on these unexploited fish that live in the darker parts of the ocean,” said Gib Brogan, a fisheries policy analyst for Oceana, a Washington-based advocacy group.
“Gold-rush fisheries don’t benefit anyone in the long term.”

Peter Auster, a marine sciences professor at the University of Connecticut who serves as a senior research scientist at the Mystic Aquarium, urged officials to prevent the findings from being put to commercial use without thoughtful regulations.
“New knowledge can lead to unforeseen consequences,” he said.
“Policymakers and management agencies need to get in front of potential problems and keep new fisheries from developing until they can assess impacts and insure sustainable use.”

At Woods Hole, the scientists leading the research acknowledged the dilemma, but they contend that the potential for new knowledge outweighs the risks.
“If large-scale harvesting starts before we understand it, that’s a recipe for disaster,” said Heidi Sosik, a Woods Hole biologist and the lead investigator of the project.

Her hope, she said, is that learning more about the region will ultimately help preserve it.
“At this point, we don’t even know basic information, such as how long the fish there live,” she said.
“Without knowing that, we can’t possibly make informed decisions about how to interact with this ecosystem in a sustainable way.”

DEEP-SEE testing at Woods Hole Oceanographic Institution.

Yet with many fisheries around the world severely depleted, new fishing grounds would be a welcome development, so long as scientists can ensure it’s done sustainably, she said.

In some cases, fishermen are already harvesting organisms that inhabit the twilight zone.
Large trawlers in recent years have been scooping up increasing quantities of crustaceans that migrate from surface waters to the deep sea, grinding their catch into fishmeal for aquaculture or pet food.

Many of those trawlers, however, are operating in international waters, beyond the reach of US law.
Sosik said she hopes the team’s findings will eventually help forge international agreements that would prevent overfishing of the twilight zone.
“If we can sustainably harvest this part of the ocean, without massively disrupting larger ocean structures, I’m all for that,” she said.
“We need high quality sources of protein, but it needs to be effective exploitation, not overexploitation.”

On a recent morning, Sosik’s team tested some of the new technology designed to peer into the great abyss.

A crane lowered one of the new instruments — a $1.2 million, 2,500-pound, specially designed system of sonars and cameras called DEEP-SEE — into a test well.
Using strobe lights, the 16-foot-longsystem has the capacity to detect microbes and other organisms as small as the width of human hair.

Being able to see such small organisms, and determine their numbers and habits with sophisticated sonar systems, should allow the researchers to better understand where the organisms migrate and what triggers their movement.
Many species in the twilight zone — everything from plankton to squid — are believed to participate every night in what the scientists call the largest migration on the planet, rising from the deep to feed near the surface before returning by daybreak to the safety of the darker, deeper sea.

That migration is believed to help regulate the planet’s climate.
As fish and other species migrate, they carry large amounts of carbon dioxide from surface waters into the deep ocean.
They do so through the cycle of small creatures ingesting phytoplankton, tiny plants that absorb carbon near the surface, and then transferring that to the larger species that eat them.

Nearly all the carbon that makes it to the deeper sea — through dead plankton, shells, and fecal matter, among other things — remains there, locking it away from being released as a heat-trapping gas into the atmosphere.

The members of the research team, which include robotocists, ecologists, chemists, and economists, also plan to study how ocean currents such as the Gulf Stream affect the twilight zone and why many of the animals there are bioluminescent, emitting colorful lights that allow them to attract mates and ward off predators.

Over the coming years, the researchers will be introducing a range of sophisticated new sensors, autonomous robots, advanced cameras, and other new tools.

For now, their immediate goal is to ensure that the new equipment works.

On Friday, they will start a 10-day expedition on a research vessel on loan from the National Oceanic and Atmospheric Administration.
The ship will travel about 150 miles south of Woods Hole to the closest deep waters, a section of the North Atlantic that’s about 6,000 feet deep.
“It’s kind of surreal that this is happening,” Sosik said.
“A year ago, it was just a dream.”
She added: “We’re hoping to learn amazing things.”